The field of this invention is air distribution and in particular air distribution in the catalyst regenerator of a fluid catalytic cracking unit.
U.S. Pat. No. 3,433,733 discloses a method and apparatus for fluid catalytic cracking of a hydrocarbon feedstock in order to produce desired reaction products. Generally, the process consists of mixing together feed stock and hot catalyst in a riser/reactor prior to entry into a tapered reactor/separator chamber. The catalyst is removed from the reactor/separator chamber in a spent condition and is directed to a regenerator wherein the carbonaceous deposit on the catalyst, referred to as "coke", is burned from the catalyst with air. The regenerated catalyst is then re-used in the process. In U.S. Pat. No. 3,433,733, an air distributor is positioned in the lower portion of the regenerator for distributing an air supply into a zone of spent catalyst in the regenerator. The efficiency of the regeneration process is dependent upon a uniform distribution of air through the spent catalyst zone. It has been found desirable to distribute the air outwardly of the air distributor at certain pressure differentials between air pressure in the distributor and air pressure in the regenerator to cause the air to effectively bubble and thus distribute through the zone of spent catalyst. However, it has also been found that the velocity of the air leaving the air ring may be so high at such desired pressure differential levels that the air actually causes some attrition of the catalyst. In order to prevent this attrition, it has been necessary to deliver the air at pressures below the higher pressure differential levels for the most efficient distribution of the air through the spent catalyst zone in the regenerator.
U.S. Pat. No. 3,912,460 discloses an air distribution system for evenly distributing air in the spent catalyst zone of a regenerator in a fluid catalytic cracking process. A horizontal distributing ring is positioned in the spent catalyst in the regenerator. The ring comprises two tapered semi-circular tubes which are interconnected at their small ends; a splitter tube joint and the two larger ends of the tapered semi-cylindrical tubes are connected to a pressurized air supply. Air is distributed outwardly into the spent catalyst zone of the regenerator through openings in the semi-cylindrical tubes.
Other patents of interest include U.S. Pat. No. 3,867,103 which discloses the utilization of Venturi-shaped nozzles for use in mixing a hydrocarbon and acid to form an emulsion in a catalytic conversion apparatus. U.S. Pat. No. 3,848,811 discloses a particular structure for a nozzle which discharges a liquid such as oil into a fluidized bed of particulate material such as catalyst in a fluid catalytic cracking system. U.S. Pat. No. 3,632,304 discloses a heater nozzle which directs combustion gas into a reactor for providing a combustion gas stream for treating catalyst. U.S. Pat. No. 3,974,091 discloses a nozzle comprising two cylinders of different diameters connected with a beveled annulus resulting in a sudden expansion at a sharp taper angle which will not permit recovery of the pressure drop due to the gas expansion. Boundary layer separation and turbulence at the expansion will counteract the pressure drop recovery due to the expansion. While this patent has a similar objective, the instant disclosure shows a unique shape resulting in greater advantages. U.S. Pat. No. 4,035,153, assignee's own patent with a few of the same inventors, merely shows a similar header support. U.S. Pat. No. 2,798,030 discloses and desires entirely different nozzles. This patent teaches that half angles of taper should be "7.degree. to 10.degree., preferably 71/2.degree. to 9.degree., and still more preferably 81/2.degree. providing a total angle of divergence or total included angle for the nozzle of 14.degree.-20.degree., 15.degree.-18.degree., and 17.degree., respectively." Instead, inventors have found the half angle of the taper may be defined at 48 as being up to but less than 7.degree., and preferably between 1.degree. and 3.5.degree. as shown in greater detail hereinafter.
The unobvious result of the newly disclosed nozzle is the higher pressure drop than that obtained in the past without increasing air blower horsepower or catalyst attrition. None of these patents disclose structure which is precisely capable of achieving the results of the invention set forth herein.